In its fullest form, it concerns the Fisher King (King Pellehan or Anfortas), the guardian of the Holy Grail, who falls into sin and consequently suffers a wound from a mystical weapon (often the Spear of Destiny from Christian eschatology). He becomes the Maimed King, and his kingdom suffers similarly, becoming the Wasteland: neither will be healed until the successful completion of the Grail Quest.
The stroke is usually described as being to the king's thighs: this has been taken as a euphemism for the genitals, which are explicitly stated to be the location of Anfortas's wound in Wolfram von Eschenbach's Parzival. In the Post-Vulgate Cycle, Thomas Malory's Le Morte d'Arthur, and later works based on those, the stroke is delivered by Sir Balin, a knight of the Round Table. He ignores an "unearthly voice" warning him off and strikes the king when he is deprived of his weapon and thinks his stroke is 'justified'.